Investment casting, particularly countergravity investment casting, utilizes pattern assemblies of the articles to be cast that are formed from a fugitive or removable material. These pattern assemblies are invested with a refractory particulate material to form a refractory shell. The fugitive material is removed from the refractory shell and the particulate material is fired to form the investment casting mold. These refractory molds are then used for investment casting of various molten metals and alloys having a shape defined by the pattern assemblies.
The pattern assemblies used in investment casting, particularly countergravity investment casting, have generally been formed by attaching one or more patterns of the article or articles to be formed to a central sprue. Each of the patterns are generally connected to the central sprue by one or more gates that are used to define passageways in the refractory mold for the purpose of feeding molten metal provided through the passageway defined in the mold by the central sprue to the various mold cavities defined by the patterns. The patterns and gates are frequently attached to a central sprue manually in a radially-extending manner as part of the patternmaking process. Where the pattern assembly is formed from wax, the patterns and gates may be attached by wax welding. While this is and has been a very effective process in many respects, the number of patterns that may be attached to the central sprue and thus the number of parts that can be made from a particular pattern assembly is generally limited by the size of the patterns, gates and sprue, and particularly by the sprue diameter, because it defines the number of patterns/gates that may be attached as well as the amount of molten material that may be supplied through the gates to the patterns. As such, pattern assemblies that utilize centralized sprues are limited with respect to their resultant casting yields by the characteristics of the sprue selected, and particularly by the sprue diameter and its length.
Since it is generally very advantageous to increase casting yields from a particular pattern assembly, the development of improved pattern assemblies, methods of making pattern assemblies, associated refractory molds and methods of making the refractory molds to provide improved castings and casting methods are very desirable.